1. Field of the Invention
The present invention relates to image forming apparatuses having ink-mist blocking mechanisms.
2. Description of the Related Art
Image forming apparatuses include printers, facsimile machines, copy apparatuses, plotters, and multifunction peripherals, an inkjet recording apparatus is known. An inkjet apparatus is an image forming apparatus of a fluid-discharging type, which discharges ink droplets onto a sheet of recording material (“recording medium”) from a recording head in a printing operation. In a serial type of an inkjet recording apparatus, the printing operation is performed while the printing head is moved in a direction (“main-scan direction”) perpendicular to the direction of transport of the sheet (“sub-scan direction”).
In the serial type of an inkjet recording apparatus, a mechanism for detecting the position of a carriage carrying the printing head and the amount of its movement is required for an accurate printing operation. In one example, the detection mechanism includes a linear encoder sheet. An inkjet recording apparatus of the serial type having such a detection mechanism using a linear encoder sheet is described below.
FIG. 13 is a plan view of a conventional inkjet recording apparatus of the serial type. The inkjet recording apparatus includes a carriage 1 on which plural printing heads 2 for discharging ink droplets are mounted. The carriage 1 is configured to be moved in the main-scan direction along a guide rod 5 by an endless timing belt 4 rotated by a motor 3. A linear encoder sheet 6 having a counter is disposed at least in a scanning area of the carriage 1 in the main-scan direction. The linear encoder sheet 6 is read by an encoder sensor 7 mounted on the carriage 1, and the scan position of the carriage 1 is detected by determining a count value read from the linear encoder sheet 6.
Each time the sheet 8 is transported by a transport mechanism 9 in the sub-scan direction by a predetermined distance, the carriage 1 is moved (or “scanned”) while the printing head 2 discharges ink droplets onto the sheet 8, forming an image thereon. Thus, the linear encoder sheet 6 is installed near the carriage 1 such that it can be reliably read by the encoder sensor 7. More specifically, the linear encoder sheet 6 is exposed along the scanning area of the carriage 1.
In the serial type of an inkjet recording apparatus, as the ink droplets are discharged via the printing head nozzle, a mist of fine ink droplets is produced. The ink mist may become attached to various portions of the apparatus due to the flow of air caused by the scanning movement of the carriage or by an electrostatic attractive force, thus contaminating the apparatus. Particularly, the ink mist may become attached to the exposed surface of the linear encoder sheet over a long period. As a result, the encoder sensor may fail to read the linear encoder sheet accurately. Such a failure to detect the carriage position affects not only the resultant image formed on the recording medium, but may also prevent an appropriate control of the carriage 1. The failure to control the carriage 1 may result in the carriage 1, which may be moved at high speed, colliding with other components within the image forming apparatus, potentially breaking them and adversely affecting the reliability or durability of the apparatus.
In order to overcome such problems, various proposals have been made. For example, Patent Document 1 discusses installing the linear encoder sheet and the encoder sensor within a cylindrical carriage unit enclosure in order to prevent the ink mist from attaching onto the linear encoder sheet. Specifically, a magnet is provided to the encoder sensor and another magnet is also provided to the carriage facing the magnet on the encoder sensor. As the two magnets are magnetically coupled to each other via the cylindrical carriage unit enclosure member, the encoder sensor can be moved along with the carriage, thus enabling the detection of the carriage position.
Patent Document 2 discusses an inkjet recording apparatus that includes plural inlets disposed within an area of movement of the carriage, plural valves for individually opening or closing the inlets, and fans producing an airflow for guiding the ink mist toward the inlets. By activating the fans and opening the inlets by the valves, an airflow is produced between the fans and the inlets, by which the ink mist is guided and eventually collected, thus preventing the attaching of the ink mist onto the linear encoder sheet.
Patent Document 3 discusses a technology for preventing the flow of ink mist from the printing head to the linear encoder sheet. The technology involves producing an airflow from the linear encoder sheet toward the carriage by using an airflow producing unit.
In the technology of Patent Document 1, the carriage and the encoder sensor are separately installed. Thus, the technology cannot be applied to the typical structure illustrated in FIG. 15 where the encoder sensor is installed on the carriage. Further, the magnetic force of the magnets by which the encoder sensor and the carriage are magnetically coupled to each other may decrease over time to such an extent that the encoder sensor and the carriage cannot be accurately positioned with respect to each other. If that happens, the carriage position cannot be accurately detected.
In the case of Patent Document 2, the linear encoder sheet is installed near the airflow produced by the fans. As a result, the ink mist may become attached to the linear encoder sheet during the ink mist collecting operation. Thus, the problem of contamination of the linear encoder sheet is not overcome.
In the case of Patent Document 3, because the airflow produced by the airflow producing unit flows from where the linear encoder sheet is installed toward the carriage, the airflow produces an external force which is directly applied to the linear encoder sheet. As a result, the linear encoder sheet may be warped or distorted, thus preventing an accurate carriage position detection.    Patent Document 1: Japanese Laid-open Patent Publication No. 2007-326257    Patent Document 2: Japanese Laid-open Patent Publication No. 2008-260154    Patent Document 3: Japanese Laid-open Patent Publication No. 2001-191604